Scientists claim that ultrasound tests are resulting in women being told their babies have died in the womb, leading them to terminate the pregnancy.
Professor Tom Bourne, from Imperial College London, said 400 viable pregnancies a year could be 'misclassified' as a miscarriage, claiming:
'These numbers are significant and relate to pregnancies that would be highly likely to reach term.'
Professor Bourne said he did not think women should be 'anxious' about the findings, but said medics need to 'get it right' so there are not 'any mistakes'.
The professor led a study which looked at 1,000 women who thought they were having a miscarriage based on pain or bleeding during the pregnancy, and subsequent scanning of the gestational sac. If there was no embryo or the foetus has no heartbeat, medics would usually diagnose a miscarriage.
But if there is doubt over whether the baby is alive, medical staff are advised to re-scan seven to ten days later, when a miscarriage will be assumed if there is no foetal growth.
But Professor Bourne's research warns that natural variation of up to 20 per cent could influence the size of the sac and so miscarriage should not be assumed.
The research - which is published in the journal, Ultrasound in Obstetrics - concludes that there should be more research, training and improved medical guidelines to reduce the chances of misdiagnosis.
Have you experienced a suspected miscarriage but actually went to term?